1. Field of the Invention
The present invention concerns a method for recording a new coded message in place of an old coded message recorded on a magnetic stripe carried by a support document by manual displacement of said document.
2. Description of the Prior Art
There are many applications where a magnetic message is to be read and modified.
This applies to prepaid transport tickets, for example. It is advantageous if the ticket read-write system is a system relying on manual displacement of the ticket as this avoids the need for a drive system requiring complex mechanical parts. Also, a manual displacement system is less vulnerable to vandalism.
However, in a manual displacement system the problem arises of the linear density of the "bits" of the magnetic code at the time of writing which must be independent of the speed and variations in the speed with which the ticket is moved across the read-write system.
French patent 2 637 102 describes a system for reading and encoding a magnetic stripe by manual displacement of the support document.
The principle of the system is that the magnetic stripe comprises a fixed coded first message followed by a variable coded second message modified each time that the ticket is passed through the read-write system. By means of a read head the fixed first message is used to synchronize the writing of the second part of the magnetic stripe by a write head.
This system has the drawback that it enables "writing" only on the second part of the magnetic stripe, the message on the first part of the stripe being invariant and used to synchronize writing on the second part of the stripe.
An object of the present invention is to enable modifiable writing on all of the length of the magnetic stripe.